Abstract:

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The application of hybrid structures or components made of dissimilar metal offers the potential to utilize the advantages of different materials often providing unique solutions to engineering requirements. However, the joining of materials by conventional welding techniques becomes difficult if the physical properties such as melting temperature and thermal expansion coefficients of the two materials are different. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. Moreover, the effect of the holding time on the microstructural evolution was investigated. The processing temperatures for the thixojoining was 1320°C and held for 5, 12, 20 and 30 minutes, respectively. The results obtained from investigating the basic geometries demonstrated a good joining quality that differs from the conventional process of welding. Metallographic analyses along the joint interface between semi-solid AISI D2 and 304 stainless steel showed a smooth transition from one to the other, with neither oxides nor microcracking being observed.

Abstract: To improve the joining efficiency of Bi-Sr-Ca-Cu-O ( BSCCO) superconducting tapes, a
new diffusion bonding technology with a direct uniaxial pressing at high temperature was
developed to join 61-filament tapes. It was observed that bonding parameters such as bonding
pressure and holding time, significantly affected the critical current ratio (CCRo). A peak CCRo
value of 89 % for the lap-joined tapes was achieved at 3 MPa for 2 h when bonding temperature
was 800 °C. Compared with the conventional diffusion bonding technology, this new technology
remarkably shortened the fabrication period and improved the superconductivity of the joints. The
bonding interface and microstructures of the joints were evaluated and correlated to the CCRo. An
uniaxial pressing at high temperature was beneficial to interface bonding, and there was an optimal
pressure value for the CCRo.

Abstract: Solid-state direct diffusion bonding between commercially pure nickel and tungsten carbide (with 6%Cobalt) has been carried out in the temperature of 980°C and 1100°C using different holding times in argon atmosphere. Samples were successfully joined without defects or cracks on the joining interface with the exception of the one joined at 980°C for 5 min. The results showed that joining occurred by the formation of a reaction zone. Scanning electron micrographs show that different intermediate layers are formed in the reaction zone, and the width of these layers increases with an increase in bonding temperature and time. Electron probe microanalysis revealed that at any particular bonding temperature, cobalt travel into the nickel side, whereas nickel travel comparatively larger distances in the tungsten carbide side.

Abstract: Using plasma alloying technique, Q235 steel was firstly treated by W-Mo-Y Multi-elements co-diffusion followed by plasma nitriding process. And then the wear tests were conducted. The effects of technological parameters on alloying layer were studied. The structure, composition, phase and micro-hardness of alloying layer were analyzed by metalloscope, XRD, SEM and microhardness tester. Results show that the microstructure of W-Mo-Y Co-diffusion layer is columnar crystal; W, Mo contents decrease from the outside to the inside. The element Y is distributed mainly at the grain boundaries. The phase of alloying layer consisted of Fe, Fe3Mo, Fe17Y2 and the solid solution of (W, Mo, Y) in α-Fe. After plasma nitriding process, the co-diffusion layer is strengthened and large amount of nitrides form and dispersedly distribute in the alloying layer. After nitriding the phase of alloying layer consist of Fe4N, Fe3Mo, Fe, MoN, Mo2N, W2N, WN. the average micro-hardness is 850HV0.05. Compared with untreated samples, the wear resistance of alloying layer is improved by 2 times under abrasive wear conditions.

Abstract: The Cu-Ce infiltration layer was formed on 304 Stainless Steel surface by double glow plasma surface metallurgy technology. The effects of source voltage and cathode voltage on surface alloying concentration, surface hardness and infiltration layer depth were analyzed by comparative test. The results showed: In the experimental range, the contents of Cu and Ce, surface hardness, deposition layer depth increase with the source voltage increasing, which is contrary to the cathode voltage; the diffusion layer depth increases with either voltage increasing in a certain range.